A dead car battery under the hood of a vehicle.

How to Recharge a Dead Car Battery Safely and Quickly

Having to recharge a dead car battery after turning the key in your vehicle and hearing not even a click from the starter is a frustrating experience — but don’t worry, because you’ve got options. In fact, there are many ways to deal with getting juice back into your car battery, but not all are appropriate for every situation.

Check out these tips on recharging that will protect both your battery and your car from further damage.

How Dead Is the Battery?

When you recharge a dead car battery, it’s very helpful to know just how dead it is before you decide how you’re going to deal with it. A healthy battery will show 12.4 to 12.7 volts across both terminals when measured with a voltmeter, a simple device that’s very handy when diagnosing battery issues.

If the voltmeter reads lower than 12.4 volts, you’ll likely run into problems when trying to start your vehicle. How much lower will determine what method you should use to charge the battery after you jump-start your vehicle and get it running again.

Above 12 Volts — Go for a Drive

In general, if the battery is showing between 12 and 12.4 volts, it’s safe to recharge it by using your vehicle’s alternator. This means driving around with as low of an electrical draw as possible — with no stereo system, no lights (don’t try this at night) and no heating or cooling functions running — to make sure that the alternator is sending as much energy into the battery as possible. You’ll also want to keep the car or truck above idle as much as possible, as higher revolutions will pour more power into the charging circuit. At least 30 minutes of driving will help charge the battery back to a safe level for your next start.

Below 12 Volts — Use a Dedicated Charger

Your vehicle’s alternator can keep a healthy battery charged, but it was never designed to completely recharge a dead car battery if the unit in question reads below 12 volts. Using the alternator to deal with such a depleted battery can actually damage your alternator. This is because it has to work overtime to fill up the battery while also dealing with the energy needs of the vehicle itself, while the vehicle is running. It’s also possible to hurt the battery by undercharging it in this way, making it less likely to keep the charge that the alternator puts into it.

With a seriously depleted battery, the best thing to do either before or immediately after a jump-start is to connect it to a dedicated battery charger. These charging devices are designed to feed electricity into a dead battery at the rate necessary to safely and deeply charge it without causing any damage. Most of the time, you can even connect your battery to one of these chargers without having to remove it from your vehicle.

Don’t take chances with your battery. Using the right recharge procedure will extend its life and ensure you don’t get stranded again.

Check out all the electrical system products available on NAPA Online or trust one of our 16,000 NAPA AutoCare locations for routine maintenance and repairs. For more information on how to recharge a dead car battery, chat with a knowledgeable expert at your local NAPA AUTO PARTS store.

Photo courtesy of Flickr.

about author

Benjamin Hunting

Having been bitten by the car bug at a young age, I spent my formative years surrounded by Studebakers at car shows across Quebec and the northeastern United States. Over ten years of racing, restoring, and obsessing over automobiles lead me to balance science writing and automotive journalism full time.  I currently contribute as an editor to several online and print automotive publications, and I also write and consult for the pharmaceutical and medical device industry.

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